Field effect transistors (FETs), which are considered semiconductor devices, have been the dominant semiconductor technology used to make application specific integrated circuit (ASIC) devices, microprocessor devices, static random access memory (SRAM) devices, and the like. In particular, complementary metal oxide semiconductor (CMOS) technology has dominated the semiconductor process industry for a number of years. Typically, silicon is the semiconductor material used in forming FETs due to cost and manufacturability. Technology advances have scaled FETs on semiconductor devices to small dimensions allowing power per logic gate to be dramatically reduced, and further allowing a very large number of FETs to be fabricated on a single semiconductor device. The speed of semiconductor devices has also increased. However, traditional silicon FETs are reaching their physical limitations as their size decreases.
There is an economic need to increase the capabilities of semiconductor devices. Most semiconductor devices are made from silicon, a group IV semiconductor material. Other semiconductor materials such as group III/V semiconductors compounds may provide advantages over group IV semiconductor materials and vice versa. For instance, Germanium (Ge), a group IV semiconductor, is an excellent p-type material for p-type field effect transistors (pFET) due to high hole mobility. However, GaAs, a group III/V semiconductor compound, has higher electron mobility when compared to silicon or germanium and thus is suited for n-type field effect transistors (nFET). In a semiconductor circuit, for example in a complementary metal-oxide semiconductor (CMOS) circuit both nFET and pFET with high performance are desired.
Combining the different groups of semiconductor materials in semiconductor structures will provide a range of performance benefits for various semiconductor devices formed on the semiconductor structures. However, problems arise when layering various semiconductor materials, especially between group III/V and group IV materials. Semiconductors are crystalline materials that have lattice structures. The different semiconductor groups and semiconductors within the same group may have varying lattice constants. When epitaxially growing a semiconductor material with a second lattice constant on a semiconductor material with a first lattice constant, defects may occur. Some of the defects may be threading dislocations. High threading dislocation density, stemming from large lattice mismatch, may render the semiconductor device unusable. Threading dislocations may occur when growing a crystal structure on another crystal structure with a different lattice constant. They are defects within the crystal structure itself.